1. Field of Invention
The present invention concerns a new and improved rack gear, and, more specifically, a hollow rack gear.
2. Discussion of Prior Art
Both manual and power assisted vehicle steering systems have used rack and pinion gears in a manner similar to that disclosed in U.S. Pat. Nos. 3,661,032; 3,693,999; and 3,709,099. The advantages of a variable ratio steering gear has been recognized (see U.S. Pat. Nos. 2,973,658; 3,064,491; and 3,267,763). These patents show variable ratio rack and pinion gear steering systems. Varying ratios have been achieved by using a gear set having variable effective pitches. The effective pitch of the rack and pinion gears can be changed by either assembling a plurality of gears in the manner disclosed in U.S. Pat. No. 2,973,658 or performing relatively expensive machining operations to form rack and/or pinion gears with a non-uniform tooth form as shown in U.S. Pat. Nos. 3,064,491 and 3,267,763.
Some of the difficulties in forming nonstandard rack gears for variable ratio steering assemblies, can be overcome by using a helical pinion gear and a rack gear having non-uniform tooth form (see U.S. Pat. No. 3,753,378). However, making a rack gear having non-uniform teeth that will mate with a helical pinion and provide a smooth variation in the gear ratio is difficult.
Additionally, known variable ratio rack and pinion steering systems have relatively heavy solid, rack gear bars. The teeth were solid and formed by metal cutting, forging or casting. The weight of a solid rack gear bar can impose substantial forces on supporting bearings, and steering linkage components when accelerated due to movement of the vehicle over a rough road or other causes. Often these forces are transmitted to the operator. Obviously, such forces can cause wear in the steering system and injury to the operator. Some rack gear bars have included a hydraulic oil passage located along the central axis thereof. Nevertheless, these bars have relatively heavy teeth and side walls which contribute to the overall weight of the rack gear.